Method of preparing potable water

Abstract

A method of removing organic carbon and other contaminants from a water stream. The method comprises screening large solids from the stream. Pre-oxidation chemicals may then be added. A coagulant is fed into the stream. An activated carbon, preferably formed from lignite, is added by pumping a highly concentrated activated carbon slurry into the stream. The stream, including the activated carbon and coagulant, next flows into a clarifier, where the coagulant will flocculate and enmesh the activated carbon. The activated carbon adsorbs organic carbon and other contaminants, including bacteria, pharmacological agents, and hydrocarbons, as the stream flows through the clarifier. Eventually, the flocculate will agglomerate and settle out in the clarifier, where it, the enmeshed carbon, and the contaminants they contain may be removed. The stream's organic carbon content exiting the clarifier will be much reduced. Accordingly, less primary oxidizing agent will be needed to treat any remaining organic carbon.

Description

BACKGROUND OF THE INVENTION[0001]Field of the Invention: The invention relates to water treatment in general and treatment of drinking water in particular.[0002]Prior Art: Much drinking water comes from surface water sources, such as rivers, lakes, and artificial impoundments or reservoirs. Water from these sources has varying degrees of impurities that must be removed or treated before the water is safe to drink. One contaminant present in many surface water sources is organic matter. Sources of organic matter include decaying plants and animals, urea, fertilizer, and other materials commonly present in surface water. Organic material in water will support bacteria. The bacteria consume oxygen as they breakdown organic material. The bacterial consumption of oxygen is measured as BOD, or biological oxygen demand. It is a key metric in assessing and treating water that is to be rendered potable. BOD should be low before water is safe to drink or, in the case of wastewater, safe to di...

AI Technical Summary

Benefits of technology

[0058]The polyacrylamide polymers increase the viscosity of slurry 11. This will help suspend much of carbon 4 in the aqueous media so that the slurry behaves like a colloidal suspension—albeit a relatively unstable one—if agitation is interrupted. Settling of the carbon particles is impeded by the viscosity of the media.

[0059]When carbon 4 does fall out of suspension in slurry 11, the formation of cake on the bottom of whatever container slurry 11 is in will be impeded. Particles that reach the bottom of the container will not have left the suspension entirely. These carbon particles will still be surrounded by the viscous aqueous media of slurry 11, including the dissolved polymers. The viscous media will inhibit the ability of the carbon to clump together. As a result, the carbon that has fallen out of suspension will remain loosely piled on the bottom of the container. This allows slurry 11 to be formed off-site and transported to the injection site for stream 1 via container, even if the container lacks agitation. While some carbon 4 will fall out of suspension, most carbon 4 may be returned to suspension simply by stirring slurry 11. No physical manipulation of the carbon 4 that has settled out, beyond stirring slurry 11, is required to return most carbon 4 to suspension.

[0060]Even after weeks with no agitation, substantially all of carbon 4 may be returned to suspension by subjecting slurry 11 to mild to moderate agitation. Bulk fluid velocities on the order of about 6 to 12 ft / min (mild agitation) are believed to be sufficient to restore carbon 4 to suspension. However, most common commercial agitators can provide agitation on the order of about 18 to 36 ft / min (moderate agitation). Agitation at these rates are more than sufficient to restore settled carbon in slurry 11 to suspension. Significantly, restoration of suspension does not require mechanical raking of carbon that has fallen out of suspension.

[0061]It will be appreciated that the ability to restore carbon 4 to suspension after a substantial interruption in the agitation of slurry 11 will facilitate the transport of slurry 11. Slurry 11 may be formed in one location and shipped substantial distances for application. As long as slurry 11 may be agitated upon arrival, slurry 11 can be pumped into stream 1 or other application. Large volumes of slurry 11 may be transported via tanker truck and then pumped out upon the application of agitation to the tanker. The use of a smooth, substantially corner free tanker with sloping sides and a sloping bottom can help restore carbon 4 to suspension. Likewise, the use of hydraulics to impart a slope to a conventional tanker can facilitate the transfer of any carbon 4 that may have settled into an area of the tanker shielded from agitation (i.e., corners and areas distal from the point of discharge).

[0062]In the preferred embodiment, carbon slurry 11 will be about 20 percent by weight (250 gm / L) activated carbon 4. When it is desired to introduce activated carbon 4 into stream 1 for treatment, activated carbon 4 may be added by pumping carbon slurry 11 directly into stream 1. By way of example, if an activated carbon concentration of 15 mg / L is desired in a water stream with a flow rate of 5500 liters per minute, only about ⅓ of a liter of 250 gm / L carbon slurry need be pumped into the stream per minute to achieve the desired concentration. Much higher carbon concentrations may be obtained in stream 1 than would be possible by mixing powdered activated carbon 4 directly into stream 1, and the method of introduction is much more convenient. Because activated carbon 4 is in aqueous slurry 11, it may be introduced with a conventional pump, such as a peristaltic metering pump or a diaphragm metering pump suitable for high viscosity fluids. If powdered activated carbon 4 were added directly, some type of solids handling system would be required, such as an induction pump. Such an attempt would be further complicated when the stream being treated is flowing, making re-circulation difficult.

[0063]After being pumped into stream 1, aqueous slurry will simply dissipate into the flowing waters of stream 1. No other introduction steps are required to incorporate the activated carbon 4 within slurry 11 into stream 1.

Problems solved by technology

One contaminant present in many surface water sources is organic matter.

However, treatment of water streams with chlorine can produce numerous chlorination disinfection by-products—many of which are undesirable.

Monitoring is required for many chlorination by-products, and excessive amounts will render water unsuitable for human consumption.

Geosmin and MIB have a very unpleasant, earthy odor.

When MIB and / or Geosmin is present in water, the taste and odor of the water can be compromised.

Other biological contaminants, such as Synura and other algae, can release chemicals that adversely effect the taste and odor of water.

Their presence can also compromise the taste and odor of water, in addition to posing a health risk if consumed.

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